Professor of Electrical Engineering Sanjeev Kulkarni (center) and Assistant Professor of Mechanical and Aerospace Engineering Clancy Rowley (far left) are collaborating on a solar energy project with Princeton Power Systems founders (from left) Erik Limpaecher, Mark Holveck and Darren Hammell. In the foreground is a solar panel similar to those that will be installed on the Engineering Quadrangle roof.

Photo: John Jameson

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Collaboration with start-up company aims to improve efficiency of solar power

Posted September 21, 2006; 03:59 p.m.

by Teresa Riordan

Solar panels that are slated to be installed this fall on the roof
of Princeton's Engineering Quadrangle will shave only about $60 off the
University's monthly electricity bill. But the technology that emerges
from this unique industry-academia research collaboration may
eventually save New Jersey households millions of dollars in energy
costs.

Princeton Power Systems, a company started in 2001 by
three freshly minted Princeton engineering graduates, has received a
grant of $529,626 from the New Jersey Commission on Science and
Technology for a collaboration with the School of Engineering and Applied Science.

"Most
people think of solar panels as being passive," said Darren Hammell,
who is chief executive officer of Princeton Power, which he cofounded
with Erik Limpaecher and Mark Holveck, all members of the class of
2001. "But we can actively control them to optimize their efficiency in
response to changing environmental conditions."

The company
produces a device called a "grid-tied inverter," which allows raw
electricity produced by a group of solar panels to flow easily into the
main power grid. It translates the direct current (DC) produced by the
solar panels into alternating current (AC) -- the form of electricity
that is the lingua franca of public utility grids -- more efficiently
than anything currently available.

Princeton Power already
produces commercial-scale inverters. One purpose of the research
project with the School of Engineering is to scale the inverter to a
smaller size so that it can work optimally for a three-bedroom house
in, say, New Brunswick.

Hammell noted that most studies of solar
power have been done in sun-saturated states like California and
Arizona. "New Jersey is in many ways ideal for solar power because of a
good state rebate program and high energy prices," he said. "But no one
has really studied how solar power can be optimized in New Jersey."

For
one thing, of course, New Jersey has a lot of clouds. This means that
in order to maximize the power harvested from the panels, the inverter
needs to tweak both the voltage (the capacity to produce electricity)
and the current (the flow of the electricity) so that both run
optimally in an on-the-fly response to changing sun intensity.

Professor of Electrical Engineering Sanjeev Kulkarni
is one of the faculty members helping Princeton Power develop robust
algorithms that will convert DC power to AC power as efficiently as
possible.

Kulkarni is no stranger to industry collaborations.
He has worked with Siemens, IBM, Intel and other big corporations on
thorny problems in image/video processing, statistical pattern
recognition and machine learning. But this is the first time he has
worked with a young company like Princeton Power.

"I'm mostly a
theoretician, but having a concrete application in mind often drives
some of the best questions in theory," said Kulkarni, whose interests
extend from signal processing to philosophy (he teaches an
undergraduate course and has cowritten a forthcoming book with
Professor of Philosophy Gilbert Harman).

Kulkarni, who also is master of Butler College, said that he and Clancy Rowley,
assistant professor of mechanical and aerospace engineering, are hoping
to inspire a team of undergraduates to focus their senior theses on the
solar power project.

"It's exciting to have this real
experimental rig to test out work that is often done through computer
simulations," said Rowley, who specializes in control theory.

Joseph
Montemarano, industrial liaison for the Princeton Institute for the
Science and Technology of Materials, also is consulting on the project.

For
the past two years, the University has been using another of Princeton
Power's products -- a beta version of a high-efficiency variable speed
fan controller -- on the cooling tower of the cogeneration plant on Elm
Road. It is one of 12 fans that chill water for 87 campus buildings.

The
company is one of a growing number of startups to emerge from
electrical engineering professor Ed Zschau's highly popular course,
"High-Tech Entrepreneurship."

Princeton Power is headquartered
in office space on the Forrestal Campus, but the young engineers
consider a couple of downtown Princeton coffee shops their auxiliary
offices of sorts. They had their first meeting with entrepreneur and
private space traveler Greg Olsen, who has invested in the company, at
Starbucks. And they often confer with Kulkarni at Small World.

The
solar panels on the Engineering Quadrangle will produce three kilowatts
of electricity, which is about what the average house in New Jersey
consumes.

Princeton Power believes that its inverters, which
have been tested in computer simulations but not yet in real-life New
Jersey weather conditions, may represent a 75 percent efficiency
improvement over other inverters currently available.

The
roof-top panels at the engineering school will be shielded by a brick
parapet. "They should be invisible from street," said Roland Heck,
associate dean for administration at the engineering school.